This invention has to do with a frame and canvas arrangement for directing airflow across a newly mined face during mining operations and is especially concerned with coal mining operations where a steady stream of air or other fluids is necessary to maintain safety conditions in the mining operation.
During mining operations such as coal mining it is mandatory to maintain a certain level of safety conditions in order to prevent injury to the miners. Two items that contribute greatly to the safety of the miner are: (1) ventilation and dust control and (2) roof control.
Ventilation and dust control are necessary because of the gasses and other debris such as dust that are released from the newly mined mineral face. Other gasses or impurities in the air may result from blasting operations in a mine, oxidation of the coal, or decay of vegetable matter such as timber. Gasses usually found in coal mines are chiefly oxygen, nitrogen, carbon dioxide, methane and sometimes carbon monoxide, hydrogen, and hydrogen sulfide. These gasses are diluted to non harmful concentrates and removed from the mine by an efficient ventilation and control system.
It is the mine face that these gasses are especially released and two items causing concern are the creation of dust and the release of methane. Dust and methane in the right concentrations can cause explosions and fires. Extreme safety conditions must prevail with these items.
In order to create a fire or explosion there must exist three essential factors: (1) a combustible material, (2) sufficient oxygen and (3) a source of ignition. Coal dust, methane and other gasses usually provide the combustible material at the face. Oxygen is provided by air circulation and the source of ignition can be many things such as the striking of the coal machinery against rock or other debris in the coal seam, or electrical arcing of the machinery controls.
Since all three of the items necessary for disaster are necessarily present at the mine face it is known that control of the concentration of the combustible material can prevent fire or explosions. Diluting the methane gas released and suppressing the coal dust are two very effective methods.
It is reported for methane to be explosive it may be in the range of 5 to 15% in an atmosphere containing sufficient amounts of oxygen.
A mixture of normal mine air containing nominal amounts of oxygen and a 5% mixture of methane can cause a rather slow explosion whereas when the mixture of methane is about 9.5% the resulting explosion or oxidation as that of the 5% methane mixture may again occur. When the atmosphere around the mine face contains more than 15% methane an explosion will probably not occur, but also any miner in such an atmosphere will have insufficient oxygen to breathe. For these reasons the methane at the coal or mineral face should be detected immediately and removed or diluted by air so as to preserve safety conditions.
Practically all dusts that are composed of carbonaceous materials are explosive. The explosion of such dusts is similiar to the burning of many small particles of dust at the same time. It is thought that the condition of dust explosions are similiar to the condition of methane explosions as described above. For this reason dust concentrations must be removed or diluted in order to preserve safety conditions.
Another important factor for safety conditions in a mine is roof support. It is reported that falls or roof account for over 50% of the fatalities that occur in coal mines in the United States.
The roof of a mine is supported by artificial means or natural means. Natural means may consist of a STRATA above the immediate coal bed roof that forms the overburden to the surface. Artificial means may include structural supports including roof bolting of the ceiling of the mine after a section or pillar has been sumped.
One of the popular methods of mining in the United States is in the use of a continuous mining machine that removes coal or minerals in the pillar method of mining. In order to perform this method of mining it is necessary to remove coal from its formation several feet forward from a supported roof condition. After removal of the coal formation the roof over the "several feet" removed is in an unsupported condition. It is important that the new coal face has air directed at it so as to remove the conditions that may cause danger to a miner and that the unsupported roof now be artifically supported. In roof bolting or other artificially supported roof conditions this means that air or other fluids must be directed to the newly mined face or materials so as to prevent the buildup of gasses or dust that might cause an explosion. In order to do this someone must extend the already existing structure of directing air underneath the naturally supported roof, or particular artifically supported roof so as to remove or dilute the gasses or dust that might be collecting.
The already existing structure for directing air to the mine face usually consists of vertical posts placed in position along the mine passageway with a temporary canvas structure strung along the posts. The canvas is one selected and/or approved by the Bureau of Mines.
Because of the importance of the already described (1) ventilation and dust control and the (2) roof control; it is important that the temporary canvas structure be extended into a newly mined section as quickly as possible after the removal of the mining machinery. The closer the air can be directed to the new face the more efficient and safer the mining operation will be. Under the existing systems a miner must trust the strata of the mine roof to support the roof until artificial supports such as roof bolts can be installed. Usually this means that the miner must enter the newly unsupported roof section to place the canvas posts and canvas so as to direct air against the face.